Deposition of Thin Films of Silicon Carbide on Fused Quartz and on Sapphire by Laser Ablation of Ceramic Silicon Carbide
- PDF / 1,220,610 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 23 Downloads / 218 Views
DEPOSITION OF THIN FILMS OF SILICON CARBIDE ON FUSED QUARTZ AND ON SAPPHIRE BY LASER ABLATION OF CERAMIC SILICON CARBIDE TARGETS
L. Rimai*, R. Ager*, J. Hangas*, E. M. Loaothetis* Nayef Abu-Ageel and M.Aslam Ford Motor Co. Research Laboratory Dept of E.E., Michigan State University
ABSTRACT Ablation of ceramic silicon carbide with 351 nm excimer radiation was used to deposit SIC films on fused silica and on sapphire. For deposition temperatures above 8500 C, diffraction shows the films to be crystalline with the [111] axis preferentially oriented normally to the film. Optical spectra show an indirect energy gap at 2.2 eV, near that for the cubic polytype, although the 200 diffractions are absent. Room temperature resistivities range between .02 to .1 Qcm. Deposition below 6000 C yields amorphous SiC with no diffraction bands, low and variable optical band gap and very high resistivity.
INTRODUCTION As a mechanically strong and chemically inert wide band gap semiconductor, SiC might be of use in electronics operatinat high temperatures and in harsh environments'. In addition to chemical vapor deposition ' , epitaxial films of SiC have been deposited recently on Si wafers by pulsed laser ablation . This p'aper reports on SiC films deposited by laser ablation on insulating substrates over a wide temperature range (300 to 11500 C) for the first time. The substrates were fused silica and sapphire, and deposition above 8500C yielded 111 textured crystalline films.
EXPERIMENTAL The pulsed laser deposition system has been described previously 5 . The ablation targets were 99.5% pure SiC ceramics (Angstrom Corp.) and were irradiated at fluences ranging from 1 to 8 J/cm2 with 351 nm XeF excimer laser radiation. For most of the depositions the fluence was 1.5J/cm2 (300 mJ over a 2 x 10 mm target area), the substrate was 7 cm from the target surface, either parallel or at 450 to it. As the target's surface would deteriorate with progressive exposure to the laser radiation (even with rotation), and as the irradiating beam quality would deteriorate with aging of the laser gas fill (even with feedback control for constant average pulse energy), intensity and direction fluctuations of the plume would increase. As a consequence the film deposition rate would decrease from run to run. The results below were obtained from experiments with sufficiently fresh laser gas fills and fresh annular areas of the target to maintain a stable plume normal to the target and to yield reproducible data. The normal to the 0.5mm thick fused quartz or (1104)-cut sapphire substrates was either at 00 or at 450 to the plume. Immediately before use, they were
ultrasonically cleaned in detergent, distilled water, 2-propanol and dried in flowing nitrogen. The heater-radiation shield configuration was the same as used earlier for the depositions on Si and temperatures were monitored through a sapphire window by a near IRpyrometer (Ircon
Mat. Res. Soc. Symp. Proc. Vol. 285. @1993 Materials Research Society
496
V1 5C1 0)6. During deposition the pyrome
Data Loading...
